It is well known that lead gasoline additives have been under attack due to environmental reasons. As a result, there has been a search for suitable octane improvers that do not employ lead. Various manganese compounds have been found and are known to improve the octane rating of gasoline compositions.
Discovery of these new manganese additives has presented additional problems in that now compatible additives must be found which alleviate problems caused by the use of manganese.
One problem encountered with the use of manganese additives is spark plug gap bridging and the resultant misfiring and engine malfunction. Another problem arises from the use of gasoline containing both manganese and lead additives. This combination results in deposits on the exhaust valve that reduce compression pressure and lead to engine malfunction due to burned exhaust valves.